1. Field of the Invention
The present invention relates to ink sets, and more particularly, relates to an ink set that is suitable for use in ink jet recording in which an ink is ejected from an orifice in response to a recording signal in order to perform recording on a recording medium, as well as to an ink jet recording apparatus, an ink jet recording method, a recording unit, and an ink cartridge.
2. Description of the Related Art
Conventionally, aqueous inks in which dyes having various color tones are dissolved in water-soluble media are used for color recording using an ink jet recording method. It is desirable that the inks exhibit the following ink jet recording characteristics (1) to (10) at as high a degree as possible.
(1) Produces images with adequate density;
(2) Satisfactorily dries on a recording medium;
(3) Smearing of the recorded image does not occur;
(4) Running of the recorded image does not occur when in contact with water, alcohols, etc.;
(5) A recorded image with superior light-fastness is produced;
(6) Does not cause clogging at nozzles;
(7) Blurring of recorded images does not occur during continuous printing or when recording is started after a long interval;
(8) Stable when stored;
(9) Problems do not occur even if inks are brought into contact with components of the recording apparatus; and
(10) Has superior heat resistance and does not affect thermal energy generation elements.
Furthermore, as demand for color ink jet recording increases, images of higher resolution and higher quality are being required. For these purposes, color images in the broad color reproduction range are achieved by selecting coloring materials having superior color developing ability, and the dot size of images is decreased by producing small ink droplets, thereby achieving images with high resolution. Furthermore, by using two or more types of inks which have different coloring material contents but the same color tone, the inks can be selected depending on the density of the image, i.e., light color portions and deep color portions, and by controlling various ink-applying processes, it is possible to produce smoother images. Using the techniques described above, ink jet recording methods have recently been producing ink jet images of high quality, which are comparable to silver halide photographs.
However, even if ink jet images of a quality comparable to silver halide photographs are produced using the techniques described above, the color balance may become unstable depending on the environment in which the images are stored and the visual appearance of the image may degrade, resulting in a loss in durability of the images. Therefore, there is an increased demand for an ink jet image which has, in addition to high resolution, even more superior durability, for example, and which does not fade substantially even if stored for a long period of time.
Accordingly, the present invention provides an ink set which can produce a color image that is able to maintain good color balance for a long period of time in which the color balance does not easily become unstable even if stored for a long time.
The present invention also provides an ink jet recording method and an ink jet recording apparatus used therefor, which can produce color images having greater durability, i.e., degradation of the visual appearance of the image is not easily recognizable even if stored for a long time.
The present invention provides a magenta ink set capable of suppressing changes in the visual color balance due to the degradation of the magenta color in images even if stored for a long time.
The present invention also provides a recording unit and an ink cartridge which can be used very effectively for the production of ink jet color images in which image degradation due to the degradation of the magenta color in images is not easily noticeable.
According to one aspect of the present invention, there is provided an ink set comprising a first aqueous ink and a second aqueous ink having the same color tone, wherein the first and second inks contain at least one common coloring material, the second ink has a lower coloring material content than the coloring material content of the first ink, and the degree of fading of an image produced with the second ink is the same as or lower than the degree of fading of an image produced with the first ink.
According to another aspect of the present invention, there is provided an ink set comprising a first aqueous ink and a second aqueous ink having the same color tone, wherein the first and second inks contain at least one common coloring material, the second ink has a lower coloring material content than the coloring material content of the first ink, and the residual rate of the reflection density of an image produced with the second ink when it is left under a condition that promotes fading is equal to or greater than that of an image produced with the first ink.
By using the ink sets as described above, it is possible to obtain color images in which the color balance does not become substantially unstable even if the image is stored for a long time.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus comprising ink storage portions storing a first aqueous ink and a second aqueous ink having a same color tone respectively, wherein the first ink and the second ink contain at least one common coloring material, the second ink has a lower coloring material content than the coloring material content of the first ink, and the degree of fading of an image produced with the second ink is the same as or lower than the degree of fading of an image produced with the first ink, and a head portion for ejecting the inks.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus comprising ink storage portions storing a first aqueous ink and a second aqueous ink having a same color tone respectively, wherein the first ink and the second ink contain at least one common coloring material, the second ink has a lower coloring material content than the coloring material content of the first ink, and the residual rate of the reflection density of an image produced with the second ink when it is left under a condition that promotes fading is equal to or greater than that of an image produced with the first ink, and a head portion for ejecting the inks.
According to a further aspect of the present invention, there is provided an ink jet recording method comprising the step of applying a first aqueous ink and a second aqueous ink having the same color tone to a recording medium, wherein the first and second inks contain at least one common coloring material, the second ink has a lower coloring material content than the coloring material content of the first ink, and the degree of fading of an image produced with the second ink is the same as or lower than the degree of fading of an image produced with the first ink.
According to a further aspect of the present invention, there is provided an ink jet recording method comprising the step of applying a first aqueous ink and a second aqueous ink having the same color tone to a recording medium, wherein the first ink and the second ink contain at least one common coloring material, the second ink has a lower coloring material content than that of the first ink, and the residual rate of the reflection density of an image produced with the second ink when it is left under a condition that promotes fading is equal to or greater than the residual rate of reflection density of an image produced with the first ink when it is left under the same conditions.
By using the apparatuses and the methods as described above, it is possible to obtain ink jet color images in which the color balance does not become substantially unstable even if stored for a long time.
According to a further aspect of the present invention, there is provided an ink set comprising a first ink and a second ink having the same color tone, wherein the second ink has a lower coloring material content than the coloring material content of the first ink, the second ink is an aqueous ink containing a dye represented by the formula (I) below as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by the formula (I) below and at least one of a dye represented by the formula (II) below and a dye represented by the formula (III) below, as coloring materials. 
In formula (I), R1 is a substituted or unsubstituted alkoxy group or a substituted or unsubstituted aryl group; each of R2 and R4 is independently a hydrogen atom or a substituted or unsubstituted alkyl group; R3 is selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, and a halogen atom; X1 is a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof; and n is 1 or 2. 
In formula (II), Ar1 is a substituted or unsubstituted phenyl group, or a substituted or unsubstituted naphthyl group; Ar2 is selected from the group consisting of an acetyl group, a benzoyl group, a 1,3,5-triazinyl group, a SO2xe2x80x94C6H5 group, and a SO2xe2x80x94C6H4xe2x80x94CH3 group; and M is selected from the group consisting of a hydrogen atom, an alkali metal, an ammonium, and an organic ammonium, M being a counter ion of the sulfonic acid group. 
In formula (III), each of Ar3 and Ar4 is independently a substituted or unsubstituted phenyl group, or a substituted or unsubstituted naphthyl group, at least one of Ar3 and Ar4 having a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof; M is selected from the group consisting of a hydrogen atom, an alkali metal, an ammonium, and an organic ammonium, M being a counter ion of the sulfonic acid group; R5 is a 1,3,5-triazinediyl group; each of R6 and R7 is independently selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, and an atomic group necessary to complete a perhydroxyazine ring together with N; and L is a bivalent organic connecting group.
According to a further aspect of the present invention, there is provided an ink set comprising a first ink and a second ink having the same color tone, wherein the second ink has a lower coloring material content than the coloring material content of the first ink, the second ink is an aqueous ink containing a dye represented by formula (I) as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by formula (I) and at least one of C. I. Acid Red 52 and C. I. Acid Red 289.
By using the first and second inks containing the coloring materials described above, it is possible to obtain color images having superior durability in which degradation over time due to the degradation of an image with magenta inks is inhibited.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus comprising ink storage portions storing a first ink and a second ink having a same color tone respectively, wherein the second ink has a lower coloring material content than the coloring material content of the first ink, the second ink is an aqueous ink containing a dye represented by formula (I) as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by formula (I) and at least one of a dye represented by formula (II) and a dye represented by formula (III), as coloring materials, and a head portion for ejecting the inks.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus comprising ink storage portions storing a first ink and a second ink having a same color tone respectively, wherein the second ink has a lower coloring material content than the coloring material content of the first ink, the second ink is an aqueous ink containing a dye represented by formula (I) as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by formula (I) and at least one of C. I. Acid Red 52 and C. I. Acid Red 289, and a head portion for ejecting the inks.
According to a further aspect of the present invention, there is provided an ink jet recording method comprising the step of applying a first ink and a second ink having the same color tone to a recording medium, wherein the second ink has a lower coloring material content than that of the first ink, the second ink is an aqueous ink containing a dye represented by formula (I) as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by formula (I) and at least one of a dye represented by formula (II) and a dye represented by formula (III), as coloring materials.
According to a further aspect of the present invention, there is provided an ink jet recording method comprising the step of applying a first ink and a second ink having the same color tone to a recording medium, wherein the second ink has a lower coloring material content than that of the first ink, the second ink is an aqueous ink containing a dye represented by formula (I) as a sole coloring material, and the first ink is an aqueous ink containing a dye represented by formula (I) and at least one of C. I. Acid Red 52 and C. I. Acid Red 289, as coloring materials.
By using the ink sets, the ink jet recording apparatuses, and the ink jet recording methods described above, it is possible to obtain ink jet color images having superior durability in which degradation of the image over time due to the degradation of an image with the magenta inks is inhibited.
According to a still further aspect of the present invention, there is provided a recording unit comprising an ink container section containing inks, and a head section for ejecting the inks, wherein the inks constitute any one of the represented ink sets used for an ink jet printer.
According to a still further aspect of the present invention, there is provided an ink cartridge comprising an ink container section containing inks, wherein the inks constitute any one of the represented ink sets.